The North Sea Basin: Early Oligocene to mid-Miocene
The lower limit of this package is defined by the basin-wide sedimentary discontinuity close to the Eocene-Oligocene boundary. This is apparently a combination of a tectonic episode, marked by inversion in areas of the North Sea Basin, with major uplift and erosion in some areas (Chapter 8), and sea-level fall consequent on the Early Oligocene cooling event(s) (Chapter 4). The temporal relationship between these events is difficult to establish owing to the widespread unconformity(ies) in this interval (Figs 72, 76 & 81). The earliest Oligocene sediments overlying this surface are characterized by extensive reworking of Eocene palynomorphs and nannofossils. In extreme cases (e.g. in Denmark), this can present significant problems in identifying the Eocene-Oligocene boundary.